The present invention relates to a torque transmission device having an outer tube with a noncircular internal circumference and an inner tube with a noncircular external circumference inserted into the outer tube, a gap being provided between the internal circumference and the external circumference. The two tubes have a predefined rotational play, and at least one elastic wire-cushion-type element is arranged in the gap between the two tubes.
A torque transmission device of the above-mentioned type is known from German patent document DE 10 2004 051 340 A1.
It is an object of the invention to modify the torque transmission device known from German patent document DE 10 2004 051 340 A1 which, in the case of a relative rotation of the two tubes, in a first angular sector, has a relatively flat characteristic curve and, adjoining the latter, an area of a pronounced characteristic curve progression, such that the torque transmission device is suitable for additional, in particular general, applications in the field of mechanical engineering.
This object is achieved by a torque transmission device having an outer tube with a noncircular internal circumference and an inner tube with a noncircular external circumference inserted into the outer tube, a gap being provided between the internal circumference and the external circumference. The two tubes have a predefined rotational play, and at least one elastic wire-cushion-type element is arranged in the gap between the two tubes. The two tubes are displaceably arranged with respect to one another in a longitudinal direction of the tubes such that they permit a length compensation also when subjected to a torque load.
Advantageous embodiments and further developments of the invention are described and claimed herein.
The invention is based on the torque transmission device known from German patent document DE 10 2004 051 340 A1, which has an outer tube with a noncircular internal circumference and an inner tube with a noncircular external circumference arranged in the outer tube. It is explicitly pointed out that, in the following description and claims, the term “inner tube” is to be understood to also apply to a rod; that is, to a component having a solid cross-section. “Non-circular” may also mean, for example, oval, polygonal, “tooth-type”, or the like. The two tubes may, for example, have a polygonal cross-section with the same number of angles. Square or triangular cross-sections, for example, are also contemplated.
A gap is provided between the two tubes. The gap may extend in the “circumferential direction” of the two tubes. As a result, the two tubes have a certain relative rotating play. Thus, for example, an “internal toothing” may be provided on the internal side of the outer tube, and an “external toothing” engaging in the “internal toothing” may be provided on the external side of the inner tube, the “toothings” having a tooth play in the circumferential direction, by which the “gap” is formed. In addition, a gap can be provided which extends in the radial direction between the two tubes.
At least one elastic wire-cushion-like element is arranged in the gap. The wire-cushion-like element provides the torque transmission device with compliance and damping characteristics and, thereby, reduces the transmission of torsional vibrations from one tube to the other or vice versa.
The term “wire-cushion-like element” should be understood in an extremely broad fashion. The wire-cushion-like element may, for example, have the structure of a braiding, a texture, or a knit. It may be made of spring wire or of a plurality of spring wires. The individual spring wires may have identical or different shapes. They may be equipped in sections or completely with a coating, for example, an elastomer, a rubberizing or the like, which provides the wire-cushion-like element with a high “internal” friction, if that is desirable. As a result, the damping characteristic can be influenced in a targeted manner with respect to the specific application.
In the case of small relative rotating angles, the at least one wire-cushion-like element has a low “spring hardness”. This means that the characteristic torsion curve of the “tube-in-tube arrangement” is flat in the case of low relative torsion angles. When the at least one wire-cushion-like element is completely compressed; that is, when it moves to “block”, the characteristic torsion curve rises steeply. Such a characteristic curve feature is advantageous for various applications.
Based on this type of arrangement which, for the most part, is known from the above-mentioned German patent document DE 10 2004 051 340A1, the invention consists of designing the torque transmission device such that, in addition to the degree of rotational freedom in the circumferential direction of the two tubes, the torque transmission device permits a “length compensation” in a longitudinal direction of the tube, specifically also during its operation, that is, also when subjected to a “torque load”, which is necessary in many uses. When correspondingly dimensioned, this type of a torque transmission device can be used, for example, in the drive train of a vehicle, in a steering drive, or in a plurality of other machine construction applications. In this case, the tubes of the torque transmission device are arranged such that, also when they are subjected to “a load”, that is, when torque is transmitted from one tube by way of the at least one wire-cushion-like element to the other tube, they are mutually displaceable in the longitudinal tube direction.
This is preferably achieved in that the internal circumference of the outer tube and the exterior circumference of the inner tube, at least over a certain tube length, each have a cross-section that remains essentially constant, which permits a mutual displacement of the two tubes, that is, a “sliding” of one tube on the other tube in the longitudinal tube direction. For this purpose, it is essential that circumferential sections of the inner tube which, when the two tubes are rotated, cause a torque transmission, are displaceable in correspondingly long “recesses” of the outer tube extending in the longitudinal direction of the tube. If the circumferential sections of the inner tube, which cause a torque transmission, each have a length “a” and if the torque transmission device is to permit a displacement path of the length “s”, the recesses in the outer tube, in which the corresponding circumferential sections of the inner tube are displaceable, should at least have a length “a+s”.
For some uses, it may also make sense to provide a “damped end stop”. Thus, for example, the axial ends of the recesses provided in the outer tube may have a conical design; that is, they may be designed to be tapering radially and/or in the circumferential direction. This may make sense, for example, when the torque transmission device is used in the drive shaft line of a vehicle. The drive shaft may be compressed in the event of a crash. A torque transmission device integrated in the drive shaft line would then be maximally pushed together, specifically farther than would be the case in normal operating situations. The torque transmitting sections of the inner tube would strike in the axial direction against the axial ends of the recesses provided in the outer tube. In order to prevent this from taking place abruptly, it may be meaningful to provide the axial ends of the recesses with a tapering design. As an alternative or in addition, damping elements, such as wire-cushion-type damping elements, rubber buffers, or the like, may also be provided for this purpose which, in such a situation, would at least to a certain extent dampen the “impacting” of the torque transmitting sections of the inner tube on the axial ends of the recesses of the outer tube.
According to a further development of the invention, it is provided that the at least one wire-cushion-like element is fixed on one of the two tubes in the axial direction. As a result, it is ensured that the at least one wire-cushion-like element is always situated in a clearly defined position. The at least one wire-cushion-like element may, for example, be fixed on the internal circumference of the outer tube or on the external circumference of the inner tube in the longitudinal direction of the tube. It may correspondingly be provided that the wire-cushion-like element is displaceable on the external side of the inner tube or on the internal side of the outer tube in the longitudinal direction of the tube. An axial fixing in each of the two directions can be achieved, for example, by use of a tube step, a shaft nut, a retaining ring, etc.
The wire cushion and the external side of the inner tube and the internal side of the outer tube, respectively, are preferably coordinated with one another such that a coefficient of friction is obtained that is as low as possible, particularly in the direction of the degree of displacement freedom, that is, in the longitudinal direction of the tube. It may also, for example, be provided that the wire-cushion-like element and the external side of the inner tube or the internal side of the outer type are provided with a low-friction coating. In addition, the wire-cushion-like element and the external side of the inner tube or the internal side of the outer tube, respectively, may be provided with a lubricant, such as a lubricating grease.
For minimizing axial friction, that is, for minimizing stick-slip effects during the axial displacement of the two tubes, the two tubes and the at least one wire-cushion-like element should be mutually coordinated such that, at least in operating conditions in which no torque or only a slight torque is transmitted, the at least one wire-cushion-like element is essentially free of radial tension and transmits hardly any radial forces (or only low radial forces) between the internal circumference of the outer tube and the external circumference of the inner tube.
Because of the low coefficient of friction between the at least one wire-cushion-like element and the external circumference of the inner tube or the internal circumference of the outer tube, there are hardly any stick-slip effects, which is important for a large number of usage possibilities, for which an axial length compensation under a torque load and a springing or damping of torsional vibrations has to take place.
In principle, it is also contemplated that at least one wire-cushion-like element is axially fixed on the external circumference of the inner tube as well as on the internal circumference of the outer tube. However, in this case, the displacement path of the two tubes is limited to the “axial elasticity path” of the wire-cushion-like element.
According to a further development of invention, the two tubes are centered relative to one another. A centering can be achieved, for example, in that circumferential sections of the internal circumference of the outer tube and/or circumferential sections of the external circumference of the inner tube are circular, in which case, the internal circumference of the outer tube in such areas rests “flatly” against the external circumference of the inner tube and can slide thereon similar to a plain thrust bearing.
As an alternative, it may be provided that only one of the two tubes has a circular design in individual circumferential sections, and the respective other tube is provided with assigned bead-type indentations or bulges which rest against these circular sections of the other tube.
In the gap between the two tubes, exactly a single elastic wire-cushion-like element may be arranged, which extends in the manner of a collar or a hose around the external circumference of the inner tube. Instead of a single hose-type “wire cushion”, a “knit band” may also be wound directly on the inner tube. As an alternative, two or more block-type or ring-segment-type wire-cushion-like elements, distributed in the circumferential direction and/or longitudinal direction of the tube, may be arranged in the gap between the two tubes. In the case of ring-type “wire cushion elements”, these may be pressed together to different degrees along the circumference, whereby the characteristic curve of the torque transmission can be optimized.
For illustrating a defined elasticity behavior, in the case of several elastic wire-cushion-like elements, these may each have different characteristic elasticity curves. The individual wire-cushion-like elements may, for example, have different shapes and/or may be made of different materials.
As indicated above, multiple shapes of the tube cross-section are contemplated. As an alternative to oval, polygonal, or toothed tube cross-sections, tubes with several beads, which are mutually spaced in the circumferential direction, can be used. The beads extend in the longitudinal direction of the tube and may, for example, be produced by internal high-pressure forming of the tubes.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.